This invention relates to a vehicle brake squeal control device for suppressing so-called squeal produced from the brakes of a vehicle during braking.
So-called brake squeals produced during braking include noises of various vibration frequencies from relatively low frequency sounds called groaning to sounds heard as irritating sounds (squeal) in a vibration band of several KHz or over. In order to eliminate or reduce them, various measures have been proposed. As one example thereof, “vehicle brake hydraulic pressure control device” of JP patent publication 9-221013 is known. This control device has means for detecting brake squeals, and a control unit for changing distribution of brake hydraulic pressures to the front and rear wheels based on squeal detection signals detected by the detecting means to control such that if brake squeals are detected, the distribution of brake hydraulic pressure will be reduced for the front wheels and increased for the rear wheels.
As another example, the “brake pressure control device” disclosed by JP patent publication 2000-168539 aims to prevent a creep groan produced during creep traveling, in which brake fluid is set at first and second predetermined pressures, and while the brake pressure decreases from the first pressure to the second pressure, which is lower than the first, the brake cylinders are connected to the reservoir through solenoid valves to reduce the pressure, thereby preventing a creep groan. In this case, a creep groan, which is produced when the brake pedal is stepped in a travel range of an automatic transmission and the pedal stepping force is slightly relaxed with the vehicle at a stop, is prevented because even though the brake pressure decreases as a result of relaxing of the pedal stepping force, the brake cylinders are kept open until the second set pressure is reached.
Actually the first and second pressures are set by detecting whether the vibration level detected by a vibration sensor is over or under a reference value, and memorizing the brake hydraulic pressure at that time as the creep groan generation starting hydraulic pressure and the creep groan disappearing hydraulic pressure. If the hydraulic pressure during next braking is not more than the creep groan generation starting hydraulic pressure, the brake hydraulic pressure is reduced, and if it is not more than the disappearing hydraulic pressure, control is carried out such that it returns to a normal braking state.
As described above, noises produced by step-in of the brake pedal by the driver during travel include noises in various frequency bands. The sensitivity of the driver for respective noises are different from one another, and thus timings at which squeal control is desired are different. Thus, it is desirable that the starting conditions of squeal reducing control, and control for reducing squeal can be set individually by the driver.
But in the control devices of the above-described publications, setting the control start conditions according to the will of the driver is not considered at all. In particular, in the control device of JP patent publication 9-221013, since a squeal is detected by a brake squeal detecting means and the squeal control is carried out based on the detection signal, if the detection of a squeal is incomplete, there is a fear that the will of the driver is not met, thus causing uncomfortableness.
Also, in the control device of JP patent publication 2000-168539, a reference level for deciding whether the squeal is above or below a predetermined level is set beforehand, and the brake hydraulic pressure range is determined with the brake hydraulic pressure corresponding thereto as the creep groan generation starting hydraulic pressure and the creep groan disappearing hydraulic pressure, and the pressure is reduced in this range to prevent a creep groan. But only with such a hydraulic pressure range, it is insufficient to estimate squeals, and thus it is impossible to eliminate uncomfortable squeals according to the will of the driver. Also, for the squeal reducing action, the device may malfunction as a result of pressure change other than squeals.
An object of this invention is to provide a brake squeal control device in which control of reducing brake squeals can be carried out according to the will of the driver, and the conditions for starting squeal reduction can be individually set to meet the requirements of the driver.